Return Value

The returned IEnumerator<T> provides the ability to iterate through the collection by exposing a Current property .You can use enumerators to read the data in a collection, but not to modify the collection.

Initially, the enumerator is positioned before the first element in the collection. At this position, Current is undefined. Therefore, you must call the MoveNext method to advance the enumerator to the first element of the collection before reading the value of Current.

If MoveNext passes the end of the collection, the enumerator is positioned after the last element in the collection and MoveNext returns false. When the enumerator is at this position, subsequent calls to MoveNext also return false. If the last call to MoveNext returned false, Current is undefined. You cannot set Current to the first element of the collection again; you must create a new enumerator instance instead.

An enumerator does not have exclusive access to the collection so an enumerator remains valid as long as the collection remains unchanged. If changes are made to the collection, such as adding, modifying, or deleting elements, the enumerator is invalidated and you may get unexpected results. Also, enumerating a collection is not a thread-safe procedure. To guarantee thread-safety, you should lock the collection during enumerator or implement synchronization on the collection.